The present invention relates to rock reinforcing apparatus and methods and, more specifically, to a combined mechanical-resin rock bolt anchoring system such as typically used in the support of mine roofs, and the like.
In mine work, such as coal mining, or in underground formations such as tunnels or excavations, it is often necessary to reinforce or support the roof and/or walls of the excavating to prevent rock falls or cave-ins. The most common means presently in use for effecting such support include elongated bolts or bars which are inserted in blind drill holes to hold a metal support plate in close engagement with the rood or wall surface. The bolt or bar is securely fixed in the hole by anchoring means such as a mechanical expansion anchor, a hardenable resin which surrounds the end of the bolt within the hole, or both.
Many variations of the basic mine roof expansion anchor have been proposed and numerous styles and models are currently in wide-spread use. Common attributes of such anchors are the expansion shell, or other such radially expansible members, and a tapered nut having a threaded opening into which one end of the rock bolt may be threadedly advanced. As the bolt is rotated with the shell and nut constrained against rotation, the nut is gradually drawn into the shell to cause radial expansion thereof into tightly engaged contact with the wall of the drill hole.
Resin anchoring is also commonly used to fixedly secure the rock bolt or bar in the drill hole. The use of polyester resins in underground formation was disclosed at least as early as the June 4, 1963, U.S. Pat. No. 3,091,935 of Brown and Pritchard entitled "Rock Treatment." It has been found expedient to provide the resin grouting materials in two components each of which remains in a semi-liquid or thixotropic phase until mixed with the other, whereupon curing progresses to the stage that the steel bolt or bar will fail before the resin bond fails. The two components, a polyester resin and a catalyst, curing or hardening agent, are commonly provided in a single cartridge wherein they are a single cartridge wherein they are physically separated in individual compartments, such as disclosed, for example, in U.S. Pat. No. 3,324,663. Upon insertion of the resin cartridge and bolt into the drill hole the rock bolt or reinforcing bar itself, or other suitable means, is used to rupture the resin cartridge and mix the two components so that the curing and hardening necessary to retain the bolt in the hole may take place.
In addition to the many varieties of mechanical anchors and resin grouting systems used individually, it has also been proposed to combine the two so that a rock bolt or reinforcing bar may be secured by both anchoring systems. Such a dual anchoring system is disclosed, for example, in Montgomery U.S. Pat. No. 3,618,326 wherein a conventional expansion anchor is used in combination with a novel two-compartment resin cartridge. Patent No. 3,702,060 likewise discloses a conventional expansion anchor threaded on the end of rock bolt and modified to carry a special resin container. Other U.S. patents, such as U.S. Pat. Nos. 2,829,502 of Demsey, 3,188,815 of Schuermann, et al, and aforementioned 3,324,663 of McLean, disclose the combination of expansible shell mechanical-type anchors with resin grouting systems.